Metallurgical approach for the development of a hot crack-resistant metal-cored wire

During the last years, the automotive industry has striven to decrease the emission rates by raising combustion temperatures in the engine. As the exhaust temperature increases, this places higher demands on the exhaust system components and the filler metals used for welding. Due to the ever increasing requirements placed on welding efficiency, the use of metal-cored stainless steel wires continues to grow. High quality can be achieved at high welding speeds with minimum amount of rework, when these wires are used. As hot cracking can occur when welding high-temperature stainless steel grades, the weldability is restricted by the resistance to solidification cracking. Within the scope of this paper, two types of metal-cored wires with significant difference in δ-ferrite and manganese contents were compared to each other concerning hot crack susceptibility. Programmable Deformation Cracking and Modified Varestraint Transvarestraint tests were performed to determine the hot cracking liability. The wire with the higher amount of δ-ferrite showed better resistance than the wire with higher manganese content. Good weldability at high welding speed was confirmed by robotic welding. Additionally, the influence of the high temperature on the formation of σ-phase and its effect on the impact toughness was investigated.